Abrasive material for shot blasting, and method for producing same

ABSTRACT

The abrasive material contains Fe, Si, Ca, Al, Mg and Mn and has an amorphous continuous phase, wherein the total amount of Fe, Si and Ca is 50.0% or more by mass in terms of the total content of FeO, SiO 2  and CaO, Fe is contained in an amount of 6.0% to 35.0% by mass inclusive in terms of FeO content, Si is contained in an amount of 15.0% to 35.0% by mass inclusive in terms of SiO 2 , and Ca is contained in an amount of 10.0% to 35.0% by mass inclusive in terms of CaO content, wherein all of the amounts are those relative to the entire amount of the abrasive material.

TECHNICAL FIELD

The present invention relates to a shot blasting abrasive material and a method for producing the same. Specifically, the invention relates to a shot blasting abrasive material that includes Fe, Si, and Ca as the main components, and a method for producing the same.

BACKGROUND ART

A steelmaking slag may be generated in a ratio of 10% to 30% by mass of a raw material when melting and refining a metal material, for example. Therefore, various methods for effectively utilizing a steelmaking slag have been studied. Steelmaking slag may be granulated into particles, and used as a filler, an abrasive material, and the like. Patent Document 1 and Patent Document 2 disclose technology that can produce particles having high crushing strength, and an abrasive material that utilizes particles prepared by granulating steelmaking slag.

PRIOR TECHNICAL DOCUMENT Patent Document

Patent Document 1: JP-A 2001-47365

Patent Document 2: JP-A 2008-45002

SUMMARY OF THE INVENTION Technical Problem

When an abrasive material having a high Fe content is produced using a steelmaking slag having a high Fe content, it may be difficult to obtain sufficient crushing strength, or a variation in crushing strength may occur. Therefore, a steelmaking slag having a low Fe content has been used to produce an abrasive material, or a slag for which the Fe content is lowered by composition adjustment has been used.

Patent Document 1 discloses shot blasting particles obtained by cooling and crushing a molten slag that is obtained by reacting a dusting inhibitor including various components with a molten reducing slag discharged from an electric steelmaking furnace. However, the Fe content in the abrasive material disclosed in Patent Document 1 is as low as 2.46% to 3.01% by mass in spite of the addition of iron oxide (e.g., scale), and Patent Document 1 is silent about an abrasive material having a high Fe content.

Patent Document 2 discloses an amorphous blasting abrasive material. However, the Fe content in the abrasive material disclosed in Patent Document 2 is 5% by mass, and Patent Document 2 is silent about an abrasive material having a high Fe content.

The present invention was conceived in view of the above situation. An object of the present invention is to provide a shot blasting abrasive material that exhibits high crushing strength while having a high Fe content in terms of FeO content of 6% to 35% by mass.

Solution to Problem

The present invention is as follows.

-   (1) A shot blasting abrasive material of claim 1 is characterized by     including Fe, Si, Ca, Al, Mg, and Mn, having an amorphous continuous     phase, having a total amount of Fe content, Si content, and Ca     content in terms of respectively FeO content, SiO₂ content, and CaO     content of 50.0% or more by mass based on 100% by mass of a total of     the shot blasting abrasive material, and having the Fe content in     terms of the FeO content of 6.0% to 35.0% by mass, the Si content in     terms of the SiO₂ content of 15.0% to 35.0% by mass, and the Ca     content in terms of the CaO content of 10.0% to 35.0% by mass. -   (2) The shot blasting abrasive material of claim 2 is characterized     by having Al content in terms of Al₂O₃ content of 3.0% to 25.0% by     mass based on 100% by mass of a total of the shot blasting abrasive     material in the shot blasting abrasive material according to claim     1. -   (3) The shot blasting abrasive material of claim 3 is characterized     by having Mn content in terms of MnO content of 2.0% to 20.0% by     mass based on 100% by mass of a total of the shot blasting abrasive     material in the shot blasting abrasive material according to claim 1     or 2. -   (4) The shot blasting abrasive material of claim 4 is characterized     by further including Ti, the shot blasting abrasive material having     Ti content in terms of TiO₂ content of 0.01% to 10.0% by mass based     on 100% by mass of a total of the shot blasting abrasive material in     the shot blasting abrasive material according to any one of claims 1     to 3. -   (5) The shot blasting abrasive material of claim 5 is characterized     by further including Cr, the shot blasting abrasive material having     Cr content in terms of Cr₂O₃ content of 0.5% to 5.0% by mass based     on 100% by mass of a total of the shot blasting abrasive material in     the shot blasting abrasive material according to any one of claims 1     to 4. -   (6) The shot blasting abrasive material of claim 6 is characterized     in that the shot blasting abrasive material is a slag particle     obtained by air-granulating a molten slag in the shot blasting     abrasive material according to any one of claims 1 to 5. -   (7) The shot blasting abrasive material of claim 7 is characterized     in that the molten slag is an electric arc furnace slag in the shot     blasting abrasive material according to claim 6. -   (8) The shot blasting abrasive material of claim 8 is characterized     in that the molten slag includes a waste glass and/or silica sand as     a composition adjustment material in the shot blasting abrasive     material according to claim 6 or 7. -   (9) The shot blasting abrasive material of claim 9 is characterized     in that the waste glass is an automotive glass in the shot blasting     abrasive material according to claim 8 -   (10) A production method of a shot blasting abrasive material is one     for the shot blasting abrasive material according to claim 6 or 7,     and is characterized by including:

an air granulation step that air-granulates a molten slag to form a slag particle;

a cooling step that cools the slag particle by spraying water to the slag particle while dropping the slag particle downward, or after dropping the slag particle; and

a dehydration/transfer step that dehydrates the slag particle while transferring the slag particle.

-   (11) A production method of a shot blasting abrasive material is one     for the shot blasting abrasive material according to claim 8 or 9,     and is characterized by including:

a composition adjustment step that adds a waste glass and/or silica sand to an electric arc furnace slag as a composition adjustment material;

an air granulation step that air-granulates the molten slag obtained through the composition adjustment step to form a slag particle;

a cooling step that cools the slag particle by spraying water to the slag particle while dropping the slag particle downward, or after dropping the slag particle; and

a dehydration/transfer step that dehydrates the slag particle while transferring the slag particle.

Advantageous Effects of the Invention

The shot blasting abrasive material of the present invention exhibits high crushing strength while having a high Fe content in terms of FeO content of 6.0% to 35.0% by mass. Therefore, it is possible to provide a shot blasting abrasive material that exhibits an excellent grinding capability, prevents breakage of the particles during grinding, produces only a small amount of dust, and has excellent reusability.

In the case where the shot blasting abrasive material is slag particles obtained by air-granulating a molten slag, since a particulate shape is obtained directly from the molten slag, high crushing strength can be obtained as compared with an abrasive material obtained by crushing a slag mass into particles. Since a steelmaking slag can be converted to the shot blasting abrasive material without loss due to crushing, high production efficiency can be achieved.

In the case where the molten slag includes waste glass as the composition adjustment material, it is possible to effectively utilize the waste glass. In the case where the waste glass is automotive glass, it is possible to effectively utilize waste automotive glass. In particular, since automotive glass obtained by scrapping automobiles has been mixed with resin parts and metal parts that are difficult to remove, it is difficult to recycle the automotive glass, and disposal by landfill is normally employed. However, the present invention can utilize automotive glass mixed with resin parts as an effective composition adjustment material, and contribute to waste reduction.

The method for producing a shot blasting abrasive material in the present invention can produce a shot blasting abrasive material that exhibits high crushing strength while having a high Fe content in terms of FeO content of 6.0% to 35.0% by mass. Therefore, it is possible to produce a shot blasting abrasive material that exhibits an excellent grinding capability, prevents breakage of the particles during grinding, produces only a small amount of dust, and has excellent reusability.

It is also possible to continuously produce the shot blasting abrasive material while achieving space conservation. The shot blasting abrasive material can be stably produced within a small space (i.e., without requiring a large space in the horizontal direction) by providing the cooling step that cools the slag particles by spraying water to the slag particles while dropping the air-granulated slag downward, or after dropping the air-granulated slag.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating the phase morphology of a shot blasting abrasive material, wherein (a) and (b) illustrate phase morphology included within the scope of the present invention, and (c) illustrates phase morphology that is not included within the scope of the present invention.

FIG. 2 is a view schematically illustrating a shot blasting abrasive material production apparatus used in Examples.

FIG. 3 is a view schematically illustrating an area of the shot blasting abrasive material production apparatus illustrated in FIG. 2 situated around an air granulation means.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the present invention will be described in detail.

1. Shot Blasting Abrasive Material

A shot blasting abrasive material of the present invention is characterized by including Fe, Si, Ca, Al, Mg, and Mn, having an amorphous continuous phase, having a total amount of Fe content, Si content, and Ca content in terms of respectively FeO content, SiO₂ content, and CaO content of 50.0% or more by mass based on 100% by mass of a total of the shot blasting abrasive material, and having the Fe content in terms of the FeO content of 6.0% to 35.0% by mass, the Si content in terms of the SiO₂ content of 15.0% to 35.0% by mass, and the Ca content in terms of the CaO content of 10.0% to 35.0% by mass.

The term “amorphous continuous phase” means that the major part of the shot blasting abrasive material is amorphous. Specifically, when the cross section of the shot blasting abrasive material is observed using an optical microscope at a magnification of 500, only one amorphous phase 1 (amorphous continuous phase 1) is observed (see (a) in FIG. 1), or a crystalline phase 2 (crystal grains having an arbitrary size) is also observed, wherein the crystalline phase 2 is enclosed by the amorphous phase 1 (continuous phase) (see (b) in FIG. 1). Specifically, when the crystalline phase 2 is also observed, the crystalline phase 2 is dispersed in the amorphous phase 1. Whether the observed phase is amorphous or crystalline is determined by X-ray diffraction measurement. Specifically, the observed phase is determined to be amorphous when the chart obtained by X-ray diffraction measurement is a halo pattern, and is determined to be crystalline when an attributable peak is observed. Examples of a crystal that may be included in the shot blasting abrasive material of the present invention and enclosed by the amorphous continuous phase 1 include a spinel crystal.

FIG. 1 (see (c)) also illustrates an example in which the amorphous continuous phase is absent. A crystalline continuous phase 3 (polycrystalline phase formed by microcrystals) is present in the example illustrated in (c) in FIG. 1. In such a case, coarse crystals 4 normally precipitate in part of the crystalline continuous phase 3. A crystalline phase 2 (e.g., spinel crystal) may also precipitate in such a case.

The shot blasting abrasive material of the present invention includes at least Fe, Si, Ca, Al, Mg, and Mn.

Further, a total amount of Fe content, Si content, and Ca content in terms of respectively FeO content, SiO₂ content, and CaO content is 50.0% or more by mass based on 100% by mass of a total of the shot blasting abrasive material of the present invention.

The shot blasting abrasive material has Fe content in terms of FeO content of 6.0% to 35.0% by mass based on 100% by mass of a total of the shot blasting abrasive material of the present invention. It has been difficult to obtain a shot blasting abrasive material having high crushing strength from a steelmaking slag having Fe content in terms of FeO content as high as 6.0% or more by mass. However, it is possible to obtain a shot blasting abrasive material having high crushing strength when the composition is within the above ranges. Specifically, it is possible to achieve a crushing strength of 20 kgf or higher when the particle size is 2.0 mm.

If the Fe content in terms of FeO content exceeds 35.0% by mass, it may be difficult to reduce a variation in crushing strength, and sufficiently maintain high crushing strength. Specifically, it may be difficult to maintain a crushing strength of 20 kgf or higher when the particle size is 2.0 mm.

The Fe content in terms of FeO content is preferably in a range from 7.0% to 32.0% by mass, more preferably from 8.0% to 30.0% by mass, further preferably from 9.0% to 28.0% by mass, and particularly from 10.0% to 26.0% by mass.

The shot blasting abrasive material has Si content in terms of SiO₂ content of 15.0% to 35.0% by mass based on 100% by mass of a total of the shot blasting abrasive material of the present invention. When the Si content is within the above range, it is possible to reduce a variation in crushing strength, and achieve high crushing strength particularly when the Fe content in terms of FeO content is as high as 6.0% to 35.0% by mass. If the Si content in terms of SiO₂ content is less than 15.0% by mass, it may be difficult to sufficiently maintain an amorphous state when the Fe content in terms of FeO content is 6.0% to 35.0% by mass. If the Si content in terms of SiO₂ content exceeds 35.0% by mass, the slag may have high viscosity in a molten state, and it may be difficult to granulate the slag.

The Si content in terms of SiO₂ content is preferably in a range from 15.0% to 34.0% by mass, more preferably from 16.0% to 33.0% by mass, further preferably from 16.0% to 32.0% by mass, furthermore preferably from 17.0% to 30.0% by mass, furthermore preferably from 18.0% to 30.0% by mass, furthermore preferably exceeds 20.0% by mass and not more than 30.0% by mass, and particularly from 21.0% to 29.0% by mass.

The shot blasting abrasive material has Ca content in terms of CaO content of 10.0% to 35.0% by mass based on 100% by mass of a total of the shot blasting abrasive material of the present invention. When the Ca content is within the above range, it is possible to reduce a variation in crushing strength, and achieve high crushing strength particularly when the Fe content in terms of FeO content is as high as 6.0% to 35.0% by mass. The shot blasting abrasive material may have Ca content in terms of CaO content of less than 10.0% by mass. Note that a slag normally has Ca content in terms of CaO content of 10.0% or more by mass. If the Ca content in terms of CaO content exceeds 35.0% by mass, the slag may have high viscosity in a molten state, and it may be difficult to granulate the slag. Moreover, the slag tends to have a high melting point.

The Ca content in terms of CaO content is preferably in a range from 11.0% to 34.0% by mass, more preferably from 12.0% to 33.0% by mass, further preferably from 13.0% to 32.0% by mass, and particularly from 15.0% to 31.0% by mass.

A total amount of Fe content, Si content, and Ca content in terms of respectively FeO content, SiO₂ content, and CaO content is 50.0% or more by mass based on 100% by mass of a total of the shot blasting abrasive material of the present invention. When the total content of FeO, SiO₂, and CaO is within the above range, it is possible to reduce a variation in crushing strength, and achieve high crushing strength particularly when the Fe content in terms of FeO content is as high as 6.0% to 35.0% by mass. Note that the total content of FeO, SiO₂, and CaO is not particularly limited, but is normally 95.0% or less by mass.

The total amount of Fe content, Si content, and Ca content in terms of the corresponding oxides above is preferably in a range from 50.0% to 95.0% by mass, more preferably from 53.0% to 90.0% by mass, further preferably from 54.0% to 85.0% by mass, and particularly from 55.0% to 80.0% by mass.

Contents of Al, Mg and Mn included in addition to the above Fe, Si and Ca, and the total content of the Al, Mg, and Mn are not particularly limited.

The Al content in terms of Al₂O₃ content is preferably in a range from 3.0% to 25.0% by mass. The shot blasting abrasive material may have Al content in terms of Al₂O₃ content of less than 3.0% by mass. Note that a slag normally has Al content in terms of Al₂O₃ content of 3.0% or more by mass. If the Al content in terms of Al₂O₃ content exceeds 25.0% by mass, the slag may have high viscosity in a molten state, and it may be difficult to granulate the slag. Moreover, the slag tends to have a high melting point.

The Al content in terms of Al₂O₃ content is preferably in a range from 3.0% to 25.0% by mass, more preferably from 4.0% to 23.0% by mass, further preferably from 5.0% to 20.0% by mass, furthermore preferably from 5.0% to 18.0% by mass, furthermore preferably from 5.5% to 18.0% by mass, furthermore preferably from 6.0% to 16.5% by mass, and particularly from 6.5% to 16.5% by mass.

The Mg content in terms of MgO content is preferably in a range from 1% to 20.0% by mass. The shot blasting abrasive material may have Mg content in terms of MgO content of less than 1.0% by mass. Note that a slag normally has Mg content in terms of MgO content of 1.0% or more by mass. If the Mg content in terms of MgO content exceeds 20.0% by mass, the slag may have high viscosity in a molten state, and it may be difficult to granulate the slag.

The Mg content in terms of MgO content is preferably in a range from 1.0% to 20.0% by mass, more preferably from 2.0% to 17.0% by mass, further preferably from 3.0% to 13.0% by mass, and particularly from 3.0% to 10.0% by mass.

The Mn content in terms of MnO content is preferably in a range from 2.0% to 20.0% by mass. The shot blasting abrasive material may have Mn content in terms of MnO content of less than 2.0% by mass. Note that a slag normally has Mn content in terms of MnO content of 2.0% or more by mass. If the Mn content in terms of MnO content exceeds 20.0% by mass, the slag may have high viscosity in a molten state, and it may be difficult to granulate the slag.

The Mn content in terms of MnO content is preferably in a range from 2.0% to 20.0% by mass, more preferably from 3.0% to 18.0% by mass, further preferably from 4.0% to 15.0% by mass, and particularly from 5.0% to 13.0% by mass.

The ratio (Mn content in terms of MnO content/Fe content in terms of FeO content) of the Mn content in terms of MnO content to the Fe content in terms of FeO content is preferably in a range from 0.26 to 1.50. When the ratio (Mn content in terms of MnO content/Fe content in terms of FeO content) is within the above range, the air-granulated slag particles have a shape close to a spherical shape. The ratio is more preferably from 0.28 to 1.00, and particularly from 0.30 to 0.90.

The shot blasting abrasive material of the present invention that includes Fe, Si, Ca, Al, Mg, and Mn (normally further includes O) may further include an additional component. Examples of the additional component include Ti, Cr, P, S, and the like. These additional components may be used either alone or in combination.

It is preferable that the shot blasting abrasive material includes Ti as the additional component. When Ti is included, it is considered that the shot blasting abrasive material becomes dense, and exhibits advantageous properties. The Ti content in terms of TiO₂ content is preferably in a range from 0.01% to 10.0% by mass. When the Ti content is within the above range, the effect of Ti can be effectively achieved.

The Ti content in terms of TiO₂ content is preferably in a range from 0.1% to 10.0% by mass, more preferably from 0.1% to 8.0% by mass, further preferably from 0.3% to 4.0% by mass, and particularly from 0.4% to 1.0% by mass.

The ratio (Ti content in terms of TiO₂ content/Fe content in terms of FeO content) of the Ti content in terms of TiO₂ content to the Fe content in terms of FeO content is preferably in a range from 0.02 to 0.10. When the ratio (Ti content in terms of TiO₂ content/Fe content in terms of FeO content) is within the above range, the air-granulated slag particles have a shape close to a spherical shape. The ratio is more preferably from 0.02 to 0.09, and particularly from 0.02 to 0.08.

The ratio (Ti content in terms of TiO₂ content/Ca content in terms of CaO content) of the Ti content in terms of TiO₂ content to the Ca content in terms of CaO content is preferably in a range from 0.04 to 0.13. When the ratio (Ti content in terms of TiO₂ content/Ca content in terms of CaO content) is within the above range, the air-granulated slag particles have a shape close to a spherical shape. The ratio is more preferably from 0.04 to 0.10, and particularly from 0.04 to 0.09.

It is preferable that the shot blasting abrasive material includes Cr in combination with Mn. When the shot blasting abrasive material includes Cr, it is considered that the shot blasting abrasive material becomes dense, and exhibits advantageous properties. The Cr content in terms of Cr₂O₃ content is preferably in a range from 0.5% to 5.0% by mass. When the Cr content is within the above range, the effect of Cr can be effectively achieved.

The Cr content in terms of Cr₂O₃ content is preferably in a range from 1.0% to 4.0% by mass, more preferably from 1.2% to 3.7% by mass, and further preferably from 1.3% to 3.5% by mass.

It is preferable that the shot blasting abrasive material of the present invention is a slag particle obtained by air-granulating a molten slag. When the shot blasting abrasive material is the slag particles obtained by air-granulating a molten slag, since a particulate shape is obtained directly from the molten slag, high crushing strength can be obtained as compared with an abrasive material obtained by crushing a slag mass into particles. Specifically, when an abrasive material is obtained by crushing a slag mass into particles, the time required for cooling increases since the slag mass is large, and it is likely that a crystalline phase is formed in the slag mass. Since the slag mass is crushed after cooling, the stress balance in the slag mass that has occurred due to cooling is easily impaired. Moreover, a latent flaw (fracture site) may be formed during crushing. As a result, the abrasive material particles may easily break due to an impact applied during grinding. On the other hand, the shot blasting abrasive material formed of the slag particles obtained by air-granulating a molten slag can be used directly as abrasive material particles while maintaining the particulate configuration obtained during cooling with high probability. Therefore, the stress balance in the slag particles obtained during cooling is maintained, and a variation in crushing strength can be reduced while maintaining higher crushing strength. Since a steelmaking slag can be converted to the shot blasting abrasive material without loss due to crushing, high production efficiency can be achieved.

It is preferable that the molten slag is an electric arc furnace slag. Specifically, a steelmaking slag is normally classified into a blast furnace slag, a converter slag, and an electric arc furnace slag. Among these, an electric arc furnace slag is preferable. The electric arc furnace slag is classified into an oxidizing slag and a reducing slag. It is preferable that the molten slag is an oxidizing slag. Specifically, it is preferable that the molten slag is an electric arc furnace oxidizing slag. Since the electric arc furnace slag (particularly electric arc furnace oxidizing slag) is characterized by its high Fe content, electric arc furnace slag is particularly suitable as the molten slag used for the shot blasting abrasive material of the present invention.

The molten slag may include waste glass and/or silica sand as a composition adjustment material. Waste glass normally includes SiO₂, CaO, Al₂O₃, Na₂O, and the like. In particular, waste glass has a high SiO₂ content and a high Na₂O content. Since waste glass is an amorphous material, and can be easily melted in the molten slag due to a low melting point, waste glass is suitable as the composition adjustment material for adjusting the composition of the molten slag.

It is preferable that the waste glass is an automotive glass. The term “automotive glass” (waste automotive glass) used herein refers to glass that has been used for automobiles, and obtained by scrapping automobiles. For example, the automotive glass may include windshield glass, rear window glass, side window glass, lamp glass, and the like either alone or in combination. Automotive glass has been normally mixed with parts other than glass. The parts other than glass refer to parts used for assembly, and include resin parts, metal parts, and the like. Since the waste automotive glass obtained by scrapping automobiles has been mixed with parts other than glass, it is difficult to recycle the waste automotive glass, and disposal by landfill is normally employed. However, when the waste automotive glass is added to a molten slag, parts other than glass do not affect the abrasive material. Specifically, when the waste automotive glass is added to a slag that is melted at a temperature as high as 1,500° C. or higher, the resin parts and the like are burnt down, and the metal parts and the like are melted, and incorporated in the slag. Since glass is an amorphous component having a low melting point, glass is smoothly melted in a molten slag with high energy efficiency, and increases the SiO₂ content in the molten slag. Since heat-treated glass that breaks into particulate pieces is normally used as automotive glass, automotive glass is particularly preferable as glass that is added to a molten slag.

The abrasive material particles included in the shot blasting abrasive material of the present invention may have a Vickers hardness of 650 Hv or higher, preferably 660 to 900 Hv, further preferably 670 to 800 Hv, and particularly 680 to 750 Hv.

Each abrasive material particle having a diameter of 2 mm or more may have a crushing strength of 18 kgf (176.4 N) or higher, or 20 kgf (196 N) or higher (particularly 30 to 70 kgf (294 to 686 N), or 45 to 60 kgf (441 to 588 N)). Note that each abrasive material particle having a diameter of 1 mm or more may have a crushing strength of 7 kgf (68.6 N) or higher (particularly 7 to 15 kgf (68.6 to 147 N), or 8 to 13 kgf (78.4 to 127.4 N)), for example. Note that a crushing strength of 1 kgf corresponds to 9.8 N.

Each value is measured using an abrasive material particle classified as “shot” defined in JIS Z 0312 (see 3.(b)). The Vickers hardness refers to the average Vickers hardness of ten randomly selected abrasive material particles measured in accordance with JIS Z 2244. The crushing strength refers to the average load value when each of ten randomly selected abrasive material particles is crushed by applying load using a universal tester.

The average particle size of the abrasive material particles included in the shot blasting abrasive material is not particularly limited. The abrasive material particles may have an average particle size appropriate for the application. The average particle size of the abrasive material particles is normally 5 mm or less. When the average particle size of the abrasive material particles is within the above range, the shot blasting abrasive material produces only a small amount of dust while maintaining high crushing strength. The average particle size of the abrasive material particles is preferably in a range from 0.05 to 4.0 mm, more preferably from 0.1 to 3.0 mm, and particularly from 0.2 to 2.0 mm. Note that the average particle size refers to the 50% particle size in the cumulative particle size distribution measured in accordance with JIS Z 8815 applied mutatis mutandis to the particle size specified in JIS Z 0312 (“Non-metallic blast-cleaning abrasives”).

2. Method for Producing Shot Blasting Abrasive Material

A method (1) in the present invention is a production method of the shot blasting abrasive material of the present invention and is characterized by including an air granulation step that air-granulates a molten slag to form a slag particle, a cooling step that cools the slag particle by spraying water to the slag particle while dropping the slag particle downward, or after dropping the slag particle, and a dehydration/transfer step that dehydrates the slag particle while transferring the slag particle.

A method (2) in the present invention is a production method of the shot blasting abrasive material of the present invention and is characterized by including a composition adjustment step that adds a waste glass and/or silica sand to an electric arc furnace slag as a composition adjustment material, an air granulation step that air-granulates the molten slag obtained through the composition adjustment step to form a slag particle, a cooling step that cools the slag particle by spraying water to the slag particle while dropping the slag particle downward, or after dropping the slag particle, and a dehydration/transfer step that dehydrates the slag particle while transferring the slag particle.

In the composition adjustment step, a waste glass and/or silica sand is added to the electric arc furnace slag as the composition adjustment material. The waste glass normally includes SiO₂, CaO, Al₂O₃, Na₂O, and the like. In particular, the waste glass has a high SiO₂ content and a high Na₂O content. Since the waste glass is an amorphous material, and can be easily melted in the molten slag due to a low melting point, the waste glass is suitable as the composition adjustment material for adjusting the composition of the molten slag.

The composition of the waste glass is not particularly limited. It is preferable that the waste glass has a total content of Si content in terms of SiO₂ content, Ca content in terms of CaO content, Al content in terms of Al₂O₃ content, and Na content in terms of Na₂O content of 70.0% or more by mass (normally 99.9% or less by mass) based on 100% by mass of the waste glass. The total content is more preferably from 55.0% to 80.0% by mass, and further preferably from 60.0% to 75.0% by mass.

It is preferable that the waste glass has a total content of Si content in terms of SiO₂ content and Na content in terms of Na₂O content of 50.0% or more by mass (normally 90.0% or less by mass) based on 100% by mass of the waste glass. The total content is more preferably from 60.0% to 90.0% by mass, and further preferably from 70.0% to 85.0% by mass. It is particularly preferable that the waste glass has Si content in terms of SiO₂ content of 50.0% or more by mass (normally 80.0% or less by mass). The content is more preferably from 55.0% to 80.0% by mass, and further preferably from 60.0% to 75.0% by mass.

The amount of the waste glass and/or silica sand added in the composition adjustment step is not particularly limited. The waste glass and/or silica sand may be added so that the resulting shot blasting abrasive material has a composition within the above ranges. Specifically, the waste glass and/or silica sand is added so that the resulting shot blasting abrasive material includes Fe, Si, Ca, Al, Mg, and Mn, has a total content of Fe content in terms of FeO content, Si content in terms of SiO₂ content, and Ca content in terms of CaO content of 50.0% or more by mass based on 100% by mass of the material, and has Fe content in terms of FeO content of 6.0% to 35.0% by mass, Si content in terms of SiO₂ content of 15.0% to 35.0% by mass, and Ca content in terms of CaO content of 10.0% to 35.0% by mass.

It is preferable that the waste glass is an automotive glass. The term “automotive glass” (waste automotive glass) used herein refers to glass that has been used for automobiles, and obtained by scrapping automobiles. For example, the automotive glass may include windshield glass, rear window glass, side window glass, lamp glass, and the like either alone or in combination. Automotive glass has been normally mixed with parts other than glass. The parts other than glass refer to parts used for assembly, and include resin parts, metal parts, and the like. Since the waste automotive glass obtained by scrapping automobiles has been mixed with parts other than glass, it is difficult to recycle the waste automotive glass, and disposal by landfill is normally employed. However, when the waste automotive glass is added to a molten slag, parts other than glass do not affect the abrasive material. Specifically, when the waste automotive glass is added to a slag that is melted at a temperature as high as 1,500° C. or higher, the resin parts and the like are burnt down, and the metal parts and the like are melted, and incorporated in the slag. Since glass is an amorphous component having a low melting point, glass is smoothly melted in a molten slag with high energy efficiency, and increases the SiO₂ content in the molten slag. Since heat-treated glass that breaks into particulate pieces is normally used as automotive glass, automotive glass is particularly preferable as glass that is added to a molten slag.

In the air granulation step, the molten slag is air-granulated to form the slag particles. The term “air granulation” refers to granulating slag using gas. The molten slag is normally air-granulated by feeding the molten slag to gas discharged from a nozzle. The shape of the nozzle, the number of nozzles, and the like are not particularly limited. For example, a ring nozzle having a plurality of nozzles that are radially placed so that the gas is discharged toward the center area, a parallel nozzle having a plurality of nozzles that are placed opposite to each other so that the gas is discharged toward the center area, or the like may be used. It is preferable to use the ring nozzle (see FIGS. 2 and 3). The ring nozzle may have a plurality of nozzles that are radially placed at equal intervals over the entire circumference. This configuration is effective for more uniformly and finely granulating the molten slag to obtain homogeneous slag particles having excellent mechanical strength.

The number of nozzles (gas outlets) provided to the ring nozzle is not particularly limited, but is normally 20 to 100, preferably 20 to 70, and more preferably 30 to 60. When the number of nozzles is within the above range, it is possible to implement stable air granulation.

The angle a of each nozzle with respect to the center part (see FIG. 3) is not particularly limited. The angle a is normally in a range from 5° to 45°, preferably from 15° to 35°, and more preferably from 20° to 30° with respect to the molten slag drop direction (normally the direction perpendicular to the ground). When the angle a is within the above range, it is possible to easily air-granulate the molten slag. It is also possible to prevent a situation in which the air-granulated slag particles move upward, and prevent a situation in which the high-temperature slag particles adhere to each other.

The gas discharge pressure from the nozzle is not particularly limited, but is normally in a range from 3 to 25 kgf/cm² per nozzle, preferably from 5 to 23 kgf/cm² per nozzle, and more preferably from 7 to 20 kgf/cm² per nozzle. When the gas discharge pressure is within the above range, it is possible to form slag particles having a small particle size. It is also possible to suppress a situation in which the air-granulated slag collides with the chamber inner wall or the like so that the slag particles have an undesired shape.

The gas discharge amount is not particularly limited, and is appropriately determined taking account of the amount and the particle size of the slag particles that are dropped, and the like. For example, when the amount of a slag melted is 2,000 to 4,000 kg (preferably 2,500 to 3,000 kg) per 60 minutes, the gas discharge amount is preferably in a range from 600 to 6,000 kl per 60 minutes, more preferably from 800 to 4,000 kl per 60 minutes, and further preferably from 1,250 to 3,500 kl per 60 minutes. The type of gas used for air granulation is not particularly limited, and various types of gases may be used. It is preferable to use air in order to simplify the structure of the apparatus.

The temperature of the molten slag is not particularly limited, but is normally in a range from 1,150° C. to 1,600° C., preferably from 1,200° C. to 1,550° C., and more preferably from 1,250° C. to 1,500° C. The type of the steelmaking slag is not particularly limited. It is preferable that the molten slag is an electric arc furnace slag. Specifically, the steelmaking slag is normally classified into a blast furnace slag, a converter slag, and an electric arc furnace slag. Among these, an electric arc furnace slag is preferable. The electric arc furnace slag is classified into an oxidizing slag and a reducing slag. It is preferable that the molten slag is an oxidizing slag. Specifically, it is preferable that the molten slag is an electric arc furnace oxidizing slag. Since the electric arc furnace slag (particularly electric arc furnace oxidizing slag) is characterized by its high Fe content, the electric arc furnace slag is particularly suitably used in the present invention.

In the cooling step, the slag particles obtained by air granulation are cooled by spraying water to the slag particles while dropping the slag particles, or after the slag particles have been completely dropped. Note that the slag particles obtained by air granulation may be cooled by spraying water to the slag particles while dropping the slag particles, and further spraying water to the slag particles that have been completely dropped. The slag particles can be moderately cooled by performing the cooling step.

The cooling step makes it possible to feed the slag particles to the dehydration/transfer step in a state in which the outer surface of the slag particles has been cooled, but the core of the slag particles has not been cooled. The thermal conductivity of the slag used in the present invention is normally about 0.3 to 2.0 W/(m·K). Therefore, it is possible to prevent a situation in which the slag particles break due to excessive cooling, and prevent a situation in which the production method becomes complex, or the size of the apparatus increases (such as when it takes time to allow the slag particles to cool, or an additional heat treatment step is required).

A water-cooling method, an air-cooling method, or the like is normally employed in a cooling step. A water-cooling method is employed in connection with the method of the present invention. When producing an abrasive material, the cooling efficiency is insufficient when using only air-cooling (e.g., natural cooling or gas spraying), and a large space (in particular a large area or a long cooling distance) is required for cooling. On the other hand, the method of the present invention can achieve a sufficient cooling effect using a small space.

In a case of the water-cooling method, a reduction in space can also be achieved by dropping the slag particles into water stored in a chamber. However, this method has a problem in that the slag particles break (i.e., deformation and cracks easily occur) since the slag particles are cooled rapidly and excessively. On the other hand, the method of the present invention can implement moderate cooling, and prevent a situation in which the slag particles break. Since the slag particles do not pass through water, and are dropped through the gas in the vertical direction, it is possible to easily allow the slag particles to have a shape close to a spherical shape. This makes it possible to easily allow the slag particles to have a shape that ensures high mechanical strength (see FIG. 2).

When using the method that drops the slag particles into water, it is necessary to close the lower end of the chamber in order to store water, and the production process is performed in a batch-wise manner. On the other hand, the method of the present invention allows the chamber to be used in an open state, and can continuously produce the abrasive material with high production efficiency (see FIG. 2). In particular, it is possible to reduce the slag storage cost when the method is employed in a steelmaking plant that is continuously operated, for example.

The drop distance during the cooling step is not particularly limited, but is normally 3 m or longer, preferably in a range from 4 to 10 m, more preferably from 4.5 to 8 m, particularly from 5 to 7 m, and normally 40 m or less. When the drop distance is within the above range, it is possible to cool the slag particles within a small space while preventing a situation in which the slag particles are insufficiently cooled. This makes it possible to efficiently produce a shot blasting abrasive material having excellent mechanical strength using a compact apparatus.

In particular, when cooling the slag particles by spraying water to the slag particles after the slag particles have been completely dropped, it is possible to prevent a situation in which the particles that have a large particle size and have not been solidified adhere to each other, so that the yield of the product can be improved. When cooling the slag particles obtained by air granulation by spraying water to the slag particles after the slag particles have been completely dropped, the slag particles that have passed through the chamber may be dropped onto a steel conveyer, and water may be sprayed to the slag particles situated on the steel conveyer while transferring the slag particles using the steel conveyer. In this case, it is preferable to spray water in the same direction (i.e., the slag particle travel direction) as the travel direction of the steel conveyer. The amount of water to be sprayed is not particularly limited. It is preferably 0.08 liter or more, more preferably in a range from 0.03 to 0.30 liter, and further preferably from 0.05 to 0.20 liter based on 1 kg of the air-granulated slag particles.

In the dehydration/transfer step, water that has adhered to the slag particles during the cooling step is removed while transferring the slag particles. The dehydration/transfer step (completely or partially) removes water from the slag particles, and dissipates heat. In the dehydration/transfer step, since the slag particles that have been subjected to the cooling step normally have heat sufficient to vaporize water, part of the water is removed by vaporization. Therefore, it is considered that heat is also removed from the slag particles during the dehydration/transfer step due to heat of vaporization of water. The temperature of the slag particles subjected to the dehydration/transfer step after the cooling step is not particularly limited, but is preferably 500° C. or higher, and more preferably in a range from 500° C. to 1,200° C.

The temperature of the slag particles collected after the dehydration/transfer step is preferably 70° C. or higher, more preferably in a range from 80° C. to 800° C., further preferably from 85° C. to 500° C., furthermore preferably from 90° C. to 200° C., and particularly from 100° C. to 150° C. When the temperature of the slag particles is within the above range, the slag particles can be kept amorphous, and exhibit particularly excellent mechanical strength. The transfer time (i.e., heat dissipation time) in the dehydration/transfer step is not particularly limited, but is normally in a range from 0.5 to 10 minutes, preferably from 0.5 to 3 minutes, and more preferably from 1 to 2 minutes. When the transfer time is within the above range, the slag particles exhibit particularly excellent mechanical strength.

The method may include an additional step other than the air granulation step, the cooling step, and the dehydration/transfer step. Examples of the additional step include a grinding step, a classification step, and the like.

The grinding step (granulation step) grinds the slag particles obtained by the dehydration/transfer step. The grinding step ensures that the slag particles having an irregular shape that are formed by a plurality of slag particles connected before being sufficiently cooled have a shape close to a spherical shape. Specifically, the slag particles having an irregular shape are divided into individual particles to have a normal shape. For example, slag particles having a shape close to a spherical shape can be obtained by grinding needle-like, whisker-like, and teardrop-like slag particles.

The classification step may be provided after the grinding step when the method includes the grinding step after the dehydration/transfer step. In the classification step, the slag particles having the desired shape and/or particle size are separated from the resulting slag particles. The classification step is normally implemented using a sieve.

The shot blasting abrasive material may be produced using an arbitrary apparatus. In order to reliably perform each step, it is preferable to use a shot blasting abrasive material production apparatus 100 (see FIGS. 2 and 3) that includes an air granulation means 110 that air-granulates a molten steelmaking slag (molten slag) 200 to form slag particles 201, a cooling means 120 that cools the slag particles 201 by spraying water to the slag particles 201 while dropping the slag particles 201, or after the slag particles 201 have been completely dropped, and a dehydration/transfer means 130 that removes water used for cooling from the slag particles 201 while transferring the slag particles 201.

The air granulation means 110 air-granulates the molten slag 200 to form the slag particles 201. The molten slag 200 is air-granulated using gas discharged from a nozzle 111. The shape of the nozzle 111 used for air granulation, the number of nozzles 111, and the like are not particularly limited. It is preferable to use a ring nozzle 110 as described above. The ring nozzle 110 may be disposed at an arbitrary position. It is preferable to dispose the ring nozzle 110 at the upper end of a chamber 121 (described below) for conserving space.

The cooling means 120 cools the slag particles 201 by spraying water to the slag particles 201 while dropping the slag particles 201, or after the slag particles 201 have been completely dropped. The cooling means 120 normally includes the chamber 121 in which the slag particles 201 are dropped, and a water spray means 124 that sprays water to the slag particles 201. The slag particles 201 can be dropped without being affected by the surrounding environment by providing the chamber 121. Note that the slag particles 201 are allowed to cool while the slag particles 201 are dropped. It is also possible to improve the cooling effect of the water spray means 124.

The shape of the chamber 121 is not particularly limited. The chamber 121 normally has a shape that is longer than is wide (see FIG. 2). When the chamber 121 has a shape that is longer than is wide, space can be conserved while providing a sufficient drop distance. The drop distance is normally 3 m or longer, preferably in a range from 4 to 10 m, more preferably from 4.5 to 8 m, particularly from 5 to 7 m, and normally 40 m or less. Therefore, the inner space of the chamber 121 normally has a vertical dimension of 3 m or more (normally 40 m or less). The cross-sectional shape of the chamber 121 in the transverse direction (i.e., the cross-sectional shape of the chamber 121 in the direction perpendicular to the direction in which the slag particles are dropped) is not particularly limited. The chamber 121 may have a circular cross-sectional shape, a rectangular cross-sectional shape, or another cross-sectional shape. It is preferable that the chamber 121 has a circular cross-sectional shape (i.e., have a cylindrical section 122 having a cylindrical shape). In this case, the slag particle collection efficiency is improved. For example, when the chamber 121 has a circular cross-sectional shape, the inner diameter (or the maximum inner length) of the main part of the chamber 121 is preferably in a range from 1 to 10 m, more preferably from 2 to 8 m, and further preferably from 3 to 6 m. It is preferable that the lower end of the chamber 121 has a narrow section 123 that narrows toward a steel conveyer 126 or the dehydration/transfer means 130. It is preferable that the lower end of the chamber 121 is open to the steel conveyer 126 or the dehydration/transfer means 130. This makes it possible to continuously produce the slag particles while ensuring the resulting slag particles have high mechanical strength.

The configuration, the size, and the like of the water spray means 124 are not particularly limited as long as the water spray means 124 can spray water to the slag particles 201. It is preferable that the water spray means 124 sprays water to the slag particles 201 over the steel conveyer 126 provided under the chamber 121 (see FIG. 2). Specifically, it is preferable to spray water to the slag particles 201 that have fallen from the chamber 121 onto the steel conveyer 126 from a water spray nozzle 125 to cool the slag particles 201.

The dehydration/transfer means 130 removes water used for cooling from the slag particles 201 while transferring the slag particles 201. Since the dehydration/transfer means 130 has both a dehydration function and a transfer function, the slag particles 201 can be continuously produced. Specifically, after cooling the slag particles 201 obtained by air granulation by spraying water to the slag particles 201 while dropping the slag particles 201, or after the slag particles 201 have been completely dropped, the slag particles 201 are dehydrated while being transferred without allowing the slag particles 201 to remain in a wet state. Therefore, since the slag particles 201 are not cooled unduly rapidly, it is possible to obtain the slag particles 201 that exhibit excellent mechanical strength. It is also possible to stably and efficiently produce the slag particles in a continuous way.

The entire dehydration/transfer means 130 may have the dehydration function and the transfer function (e.g., when the entire dehydration/transfer means 130 is formed by a wedge wire screen 132), or only part of the dehydration/transfer means 130 may have the dehydration function and the transfer function, and the remainder of the dehydration/transfer means 130 may have only the transfer function (e.g., when the front part of the dehydration/transfer means 130 is formed by a wedge wire screen, and the rear part of the dehydration/transfer means 130 is formed by a heat-resistant conveyer such as a steel conveyer). Specifically, even when the rear part of the dehydration/transfer means 130 has only the transfer function, water is vaporized due to heat possessed by the slag particles 201 while heat is dissipated. When the slag particles 201 that are dehydrated and transferred by the dehydration/transfer means 130 has a temperature sufficient to vaporize water (e.g., 80° C. or higher, and preferably 100° C. or higher), slag particles having higher mechanical strength are normally obtained as compared with the case where the slag particles 201 have been cooled to a temperature insufficient to vaporize water (e.g., lower than 70° C.).

It is preferable that the temperature of the slag particles 201 that have been transferred from the cooling means 120 to the dehydration/transfer means 130 is 800° C. or higher. In the dehydration/transfer means 130, a cooling rate of the slag particles 201 (normally allow the slag particles 201 to cool) is preferably in a range from 130° C. to 600° C. per minute, more preferably from 150° C. to 400° C. per minute, further preferably from 180° C. to 300° C. per minute, and particularly from 180° C. to 250° C. per minute, . When the cooling rate is within the above range, the transfer distance can be reduced while ensuring sufficient dehydration and cooling, and an improvement in product quality and space conservation can be particularly effectively achieved in combination.

When the rear part of the dehydration/transfer means 130 has only the transfer function (transfer section), the transfer section may transfer the slag particles in the horizontal direction, or may transfer the slag particles in the vertical direction. For example, the dehydration/transfer means 130 may include a bucket conveyer 134 or the like. This makes it possible to achieve further space conservation.

The configuration of the dehydration/transfer means 130 is not particularly limited. It is preferable that the dehydration/transfer means 130 includes the wedge wire screen 132 as at least part of the dehydration/transfer means 130, the wedge wire screen 132 including wedge wires 131 that are arranged at intervals at which the slag particles 201 cannot pass through. When the dehydration/transfer means 130 includes the wedge wire screen 132 as only part of the dehydration/transfer means 130, it is preferable that the wedge wire screen 132 is provided on the front side (i.e., the side close to the cooling means) of the dehydration/transfer means 130. The wedge wire screen 132 can dehydrate and transfer the slag particles 201 using a simple configuration.

The configuration of the wedge wires 131 used for the wedge wire screen 132 is not particularly limited. When the average particle size of the desired slag particles 201 is 5 mm or less, wedge wires 131 at intervals of preferably in a range from 0.1 to 4.0 mm, more preferably from 0.1 to 1.0 mm, and further preferably from 0.2 to 0.5 mm is used. In this case, it is possible to easily obtain the slag particles 201 having a shape closer to a spherical shape without performing the grinding step (granulation step).

When using the wedge wire screen 132, it is preferable that the wedge wire screen 132 is able to achieve dehydration by applying vibrations. It is preferable that the wedge wire screen 132 is able to transfer the slag particles 201 by applying vibrations. Therefore, it is preferable that the dehydration/transfer means 130 includes a vibration generation means 133, and vibrations generated by the vibration generation means 133 is transmitted to the wedge wire screen 132.

The apparatus 100 may include an additional means other than the air granulation means 110, the cooling means 120, and the dehydration/transfer means 130. Examples of the additional means include a molten slag storage means 150 that feeds an appropriate amount of a molten slag 200 to the air granulation means 110. The molten slag storage means 150 may include a heating means 152 (e.g., burner and/or heater) in order to prevent a situation in which the stored molten slag 200 cools. A tundish 150 is normally used as the molten slag storage means 150. The capacity, the shape, and the like of the tundish 150 are not particularly limited. It is preferable that the tundish 150 has a lower opening through which the molten slag can flow downward. It is preferable that the opening has a circular shape. An inner diameter thereof is preferably in a range from 10 to 50 mm, more preferably from 12 to 35 mm, and further preferably from 16 to 28. A depth of the tundish 150 is preferably in a range from 50 to 200 cm, more preferably from 70 to 150 cm, and further preferably from 80 to 120 cm. The flow rate of the molten slag from the tundish 150 is preferably in a range from 5 to 40 l/min, more preferably from 7 to 30 l/min, and further preferably from 8 to 15 l/min.

The apparatus 100 may include a transfer water spray means that sprays water to cool the slag particles 201 transferred by the dehydration/transfer means 130 as the additional means. The configuration and the like of the transfer water spray means are not particularly limited. For example, a water spray pipe may be provided parallel to the dehydration/transfer means 130 (e.g., wedge wire screen 132).

The apparatus 100 may include a heat exchange means as the additional means. The heat exchange means recovers heat released within the apparatus (shot blasting abrasive material production apparatus 100) when the molten slag 200 is converted to the slag particles 201. The configuration and the like of the heat exchange means are not particularly limited. The heat exchange means (heat recovery means) may be implemented by providing a known heat recovery device at an appropriate position of the apparatus (e.g., chamber 121 or tundish 150). It is possible to efficiently utilize waste heat, and improve the cooling efficiency by providing the heat recovery means.

The apparatus 100 may include a grinding means that performs the grinding step as the additional means. An Eirich mixer, a mortar mixer, or the like may be used as the grinding means. The apparatus 100 may include a classification means that follows the grinding means. A vibrating screen, a mono layer, or the like may be used as the classification means.

EXAMPLES

Hereinafter, the present invention is specifically described using Examples.

-   [1] Production of shot blasting abrasive material

A shot blasting abrasive material 201 was produced using the shot blasting abrasive material production apparatus 100 (see FIG. 2) including the structure (i.e., the structure situated around the air granulation means 110) illustrated in FIG. 3.

The shot blasting abrasive material production apparatus 100 illustrated in FIG. 2 includes the air granulation means 110, the cooling means 120, the dehydration/transfer means 130, and a collection container 141. The shot blasting abrasive material production apparatus 100 includes the molten slag storage means (tundish) 150 that precedes the air granulation means 110. Almost the entirety of the production apparatus 100 is placed in an underground pit. Leakage of operating noise can be reduced by placing the production apparatus 100 underground.

The molten slag storage means 150 is a tundish. The tundish 150 is in the shape of a rectangular parallelepiped (200 cm×100 cm×100 cm (depth). A nozzle formed of a refractory material is attached to the bottom of the tundish 150. The tundish 150 has an opening 151 having a diameter of about 24 mm so that the molten slag 200 can be fed to the air granulation means 110. A burner 152 that can adjust the temperature of the molten slag 200 stored in the tundish 150 is provided. A weir and a damper (not illustrated in FIG. 2) are also provided in order to prevent entrance of a massive foreign substance.

The air granulation means (ring nozzle) 110 includes a ring nozzle (diameter: 30 cm) in which forty-five nozzles 111 are radially arranged to be inclined toward the center. The angle a (see FIG. 3) of each nozzle is set to 26° to 27°.

The cooling means 120 includes the chamber 121, the water spray means 124, and the steel conveyer 126. The chamber 121 has a tubular shape, and includes the cylindrical section 122 having a diameter of 400 cm and a length of 4.3 m, and the narrow section 123 that extends from the cylindrical section 122, and has a lower-end diameter of 150 cm and a length of 1.4 m. The drop distance of the air-granulated slag from the air granulation means is 5.7 m. The water spray means 124 includes the water spray nozzle 125. The water spray nozzle 125 is provided over the steel conveyer 126, and sprays water to the slag particles 201 that have fallen from the chamber 121 onto the steel conveyer 126. The steel conveyer 126 is provided under the chamber 121. The slag particles 201 that have fallen from the chamber 121 are transferred to the wedge wire screen 132 through the steel conveyer 126.

The dehydration/transfer means 130 includes the wedge wire screen 132 (length: 3 m) in which the wedge wires 131 having an inverted triangular shape are arranged at intervals of 0.2 mm, and the bucket conveyer 134 (vertical length: 12.5 m). The wedge wire screen 132 is connected to a vibration generation device 133, and vibrated at about 60 Hz (vibration (45° (upward) with respect to the travel direction) width: 6 mm). The air-granulated slag 201 that has fallen from the cooling means is dehydrated and transferred on the wedge wire screen 132 due to vibrations (transfer speed: about 12 m/min). The bucket conveyer 140 moves the air-granulated slag 201 transferred from the wedge wire screen 132 upward from the underground pit to the collection container 141 situated on the ground. The bucket conveyer 140 has a transfer length of 9 m in the vertical direction.

-   [2] Production of shot blasting abrasive material

(1) Experimental Examples 1 to 6 and 12 to 16

A shot blasting abrasive material was produced as described below using a steelmaking slag (electric arc furnace slag) as a raw material utilizing the shot blasting abrasive material production apparatus 100 (see [1]).

About 3 tons of a molten slag 200 obtained from an electric arc furnace was put in the tundish 150 of the production apparatus 100 (see [1]).

The molten slag 200 flowed into the chamber 121 through the bottom opening of the tundish 150, and passed through the center part of the ring nozzle 110. Air was discharged from the ring nozzle 110 at a gas discharge pressure of 16 kgf/cm². The molten slag 200 passing through the ring nozzle 110 was air-granulated to have a particulate shape, and fell inside the chamber 121. The air-granulated slag 201 was air-cooled inside the chamber 121.

The air-cooled air-granulated slag 201 was discharged to the steel conveyer 126 from the narrow section 123. The water spray means 125 sprayed cooling water (3 l/min) to the air-granulated slag 201 at a water spray pressure of about 0.3 to 0.4 MPa, and the air-granulated slag 201 fell on to the wedge wire screen 132 of the dehydration/transfer means 130.

The air-granulated slag 201 was dehydrated on the wedge wire screen 132, and sequentially transferred to the bucket conveyer 140 due to vibrations. The air-granulated slag 201, immediately after falling onto the steel conveyer 126, had a dusky-red color when observed with the naked eye. It was thus confirmed that the temperature of the air-granulated slag 201 was about 1000° C. The transfer time on the wedge wire screen having a length of 3 m was 0.25 minutes. The air-granulated slag 201 was transferred by the bucket conveyer 140 at a speed of 8 m/min, and collected by the collection container 141. The temperature of the air-granulated slag immediately after collection by the collection container was 99.5° C.

The slag particles 201 were removed from the collection container 141, put in a grinding device, and ground for 2 minutes at an agitator rotational speed of 800 rpm and a pan rotational speed of 85 rpm. The slag particles were passed through a sieve having a mesh size of 0.2 mm to collect a shot blasting abrasive material.

(2) Experimental Example 7 Composition Adjustment using Silica Sand

Silica sand (Si content in terms of SiO₂ content: 93.1% by mass, Al content in terms of Al₂O₃ content: 1.8% by mass) was added to a steelmaking slag (electric arc furnace slag) utilizing the shot blasting abrasive material production apparatus 100 (see [1]) in a ratio of 0.845 tons per 10 tons of the steelmaking slag to obtain a molten slag 200 (i.e., the composition was adjusted using silica sand).

A shot blasting abrasive material was produced in the same manner as in Experimental Examples 1 to 6 and 12 to 16, except that the molten slag of which the composition was adjusted using silica sand, was used.

(3) Experimental Examples 8 to 11 Composition Adjustment using Waste Automotive Glass

The waste glass obtained by scrapping automobiles was added to a steelmaking slag (electric arc furnace slag) utilizing the shot blasting abrasive material production apparatus 100 (see [1]) in a ratio of 1 ton per 10 tons of the steelmaking slag to obtain the molten slag 200 (i.e., the composition was adjusted using the waste automotive glass). Note that the waste automotive glass (glass component) had an Si content in terms of SiO₂ content of 67.7% by mass, an Na content in terms of Na₂O content of 12.6% by mass, an Al content in terms of Al₂O₃ content of 2.0% by mass, and a Ca content in terms of CaO content of 9.5% by mass.

A shot blasting abrasive material was produced in the same manner as in Experimental Examples 1 to 6 and 12 to 16, except that the molten slag of which the composition was adjusted using the waste automotive glass, was used.

TABLE 1 Experimental Content in terms of oxide (% by mass) Example FeO SiO₂ CaO Al₂O₃ MgO MnO Cr₂O₃ TiO₂ Fe + Si + Ca Mn/Fe Ti/Fe Ti/Ca 1 13.3 18.3 28.3 15.3 6.6 10.6 2.2 0.4 59.9 0.80 0.03 0.08 2 18.1 23.6 27.2 12.8 5.0 6.1 1.8 0.8 68.9 0.34 0.04 0.06 3 16.3 25.7 24.7 11.2 6.5 7.5 2.3 1.2 66.7 0.46 0.07 0.06 4 18.9 28.5 23.7 6.7 6.5 11.1 1.9 0.7 71.1 0.59 0.04 0.05 5 15.3 28.3 22.9 9.5 8.5 10.5 1.8 0.7 66.5 0.69 0.05 0.07 6 24.7 24.4 16.1 10.3 7.2 8.3 3.4 0.6 65.2 0.34 0.02 0.04 7 19.3 18.8 26.3 15.3 5.5 5.9 1.9 0.8 66.5 0.31 0.04 0.05 8 16.3 20.7 24.5 14.0 8.0 7.4 2.3 0.7 61.5 0.45 0.04 0.06 9 21.4 19.1 26.9 12.5 5.2 6.4 2.7 0.6 67.4 0.30 0.03 0.05 10 18.8 24.8 28.5 10.2 4.4 6.1 2.0 0.6 72.1 0.32 0.03 0.05 11 11.1 27.7 27.4 11.1 6.7 8.3 2.8 0.7 66.2 0.75 0.06 0.09 12 *46.6  *10.6  14.6 8.9 4.3 6.7 1.8 0.3 71.8 0.14 0.01 0.02 13 23.8 *12.0  35.5 10.0 4.0 5.8 1.9 0.2 71.3 0.24 0.01 0.04 14 26.2 *12.3  26.4 14.2 5.0 6.7 2.3 0.4 64.9 0.26 0.02 0.04 15 *35.9  16.4 15.3 10.8 5.6 6.3 3.1 0.4 67.6 0.18 0.01 0.03 16 30.6 *13.3  20.0 13.3 6.3 7.6 1.7 0.9 63.9 0.25 0.03 0.03 Experimental Composition adjustment Crushing strength Vickers hardness Amorphous Example material (kgf/particle) (Hv) continuous phase 1 — 22 709 Present 2 — 31 724 Present 3 — 30 724 Present 4 — 21 723 Present 5 — 36 745 Present 6 — 25 728 Present 7 Silica sand 20 722 Present 8 Waste glass 28 723 Present 9 Waste glass 22 718 Present 10 Waste glass 20 717 Present 11 Waste glass 24 723 Present 12 — 5 889 Absent 13 — 7 868 Absent 14 — 10 811 Absent 15 — 10 775 Absent 16 — 10 795 Absent

“Fe+Si+Ca” in Table 1 indicates a total content of Fe content in terms of FeO content, Si content in terms of SiO₂ content, and Ca content in terms of CaO content.

“Mn/Fe” in Table 1 indicates a ratio of “Mn content in terms of MnO content/Fe content in terms of FeO content”.

“Ti/Fe” in Table 1 indicates a ratio of “Ti content in terms of TiO₂ content/Fe content in terms of FeO content”.

“Ti/Ca” in Table 1 indicates a ratio of “Ti content in terms of TiO₂ content/Ca content in terms of CaO content”.

[3] Evaluation of Shot Blasting Abrasive Material (1) Component Analysis

Each of the shot blasting abrasive materials obtained in Experimental Examples 1 to 16 was ground using a vibrating mill, and the resulting powder was compacted to obtain a sample. The components of the sample were analyzed using a multi-channel X-ray fluorescence spectrometer system (“Simultix 10” manufactured by Rigaku Corporation). The results are shown in Table 1.

(2) Crushing Strength

Spherical abrasive material particles classified as “shot” defined in JIS Z 0312 (see 3.(b)) and having a particle size of 2 mm (2.0±0.1 mm (measured using digital calipers)) were selected from each of the shot blasting abrasive materials obtained in Experimental Examples 1 to 16. The crushing strength (i.e., the load value when each abrasive material particle was crushed by applying load) of each of ten randomly selected abrasive material particles was measured using a crushing strength measurement device (“Amsler-type universal tester AU-30” manufactured by Tokyo Koki Co., Ltd.), and the average value of the resulting data was calculated. The results are shown in Table 1.

(3) Vickers Hardness

Spherical abrasive material particles classified as “shot” defined in JIS Z 0312 (see 3.(b)) and having a particle size of 2 mm (2.0±0.1 mm (measured using digital calipers)) were selected from each of the shot blasting abrasive materials obtained in Experimental Examples 1 to 16. The Vickers hardness of each of ten randomly selected abrasive material particles was measured (in accordance with JIS Z 2244) using a Vickers hardness meter (“MVK” manufactured by Akashi Seisakusho), and the average value of the resulting data was calculated. The results are shown in Table 1.

(4) Presence or Absence of Amorphous Continuous Phase

Spherical abrasive material particles classified as “shot” defined in JIS Z 0312 (see 3.(b)) and having a particle size of 2 mm (2.0+0.1 mm (measured using digital calipers)) were selected from each of the shot blasting abrasive materials obtained in Experimental Examples 1 to 16. Each of ten randomly selected abrasive material particles was cut, and the surface thereof was polished. The polished surface was observed using an optical microscope at a magnification of 500 to determine the presence or absence of an amorphous continuous phase. A case (experimental example) where each of the ten samples had an amorphous continuous phase is indicated by “Present” in Table 1. A case (experimental example) where at least one of the ten samples did not have an amorphous continuous phase is indicated by “Absent” in Table 1.

REFERENCE SIGNS LIST

1: amorphous continuous phase, 2: crystalline phase, 3: crystalline continuous phase (polycrystalline phase), 4: crystalline phase (coarse crystal), 100: shot blasting abrasive material production apparatus, 110: air granulation means (ring nozzle), 111: nozzle, 120: cooling means, 121: chamber, 122: cylindrical section, 123: narrow section, 124: water spray means, 125: water spray nozzle, 126: steel conveyer, 130: dehydration/transfer means, 131: wedge wire, 132: wedge wire screen, 133: vibration generation means (vibration generation device), 140: bucket conveyer, 141: collection container, 150: molten slag storage means (tundish), 151: opening of molten slag storage means, 152: heating means (burner), 200: molten slag, 201: slag particles (shot blasting abrasive material) 

1. A shot blasting abrasive material characterized by comprising Fe, Si, Ca, Al, Mg, and Mn, having an amorphous continuous phase, having a total amount of Fe content, Si content, and Ca content in terms of respectively FeO content, SiO₂ content, and CaO content of 50.0% or more by mass based on 100% by mass of a total of the shot blasting abrasive material, and having the Fe content in terms of the FeO content of 6.0% to 35.0% by mass, the Si content in terms of the SiO₂ content of 15.0% to 35.0% by mass, and the Ca content in terms of the CaO content of 10.0% to 35.0% by mass.
 2. The shot blasting abrasive material according to claim 1, having Al content in terms of Al₂O₃ content of 3.0% to 25.0% by mass based on 100% by mass of a total of the shot blasting abrasive material.
 3. The shot blasting abrasive material according to claim 1, having Mn content in terms of MnO content of 2.0% to 20.0% by mass based on 100% by mass of a total of the shot blasting abrasive material.
 4. The shot blasting abrasive material according to claim 1, further comprising Ti, the shot blasting abrasive material having Ti content in terms of TiO₂ content of 0.01% to 10.0% by mass based on 100% by mass of a total of the shot blasting abrasive material.
 5. The shot blasting abrasive material according to claim 1, further comprising Cr, the shot blasting abrasive material having Cr content in terms of Cr₂O₃ content of 0.5% to 5.0% by mass based on 100% by mass of a total of the shot blasting abrasive material.
 6. The shot blasting abrasive material according to claim 1, wherein the shot blasting abrasive material is a slag particle obtained by air-granulating a molten slag.
 7. The shot blasting abrasive material according to claim 6, wherein the molten slag is an electric arc furnace slag.
 8. The shot blasting abrasive material according to claim 6, wherein the molten slag includes a waste glass and/or silica sand as a composition adjustment material.
 9. The shot blasting abrasive material according to claim 8, wherein the waste glass is an automotive glass.
 10. A method for producing the shot blasting abrasive material according to claim 6, comprising: an air granulation step that air-granulates a molten slag or an electric arc furnace slag to form a slag particle; a cooling step that cools the slag particle by spraying water to the slag particle while dropping the slag particle downward, or after dropping the slag particle; and a dehydration/transfer step that dehydrates the slag particle while transferring the slag particle.
 11. A method for producing the shot blasting abrasive material according to claim 8, comprising: a composition adjustment step that adds a waste glass and/or silica sand to a molten slag or an electric arc furnace slag as a composition adjustment material; an air granulation step that air-granulates the molten slag or the electric arc furnace slag obtained through the composition adjustment step to form a slag particle; a cooling step that cools the slag particle by spraying water to the slag particle while dropping the slag particle downward, or after dropping the slag particle; and a dehydration/transfer step that dehydrates the slag particle while transferring the slag particle. 